When you think about it, this is actually totally useless. It is much easier to just generate a puzzle on the fly

Serious Sudoku players tend to scorn machine-generated puzzles and regard those build by Sudoku masters as superior. See for example http://www.nikoli.co.jp/en/puzzles/sudoku/hand_made_sudoku.h...

I believe similar arguments are made by crossword fans, though it is easier to understand why in that case.

So I can see the motivation for the application, at least.